Pros
The biggest "pro" I've found at Draper is that I have the opportunity to work with some of the smartest people in the world. The work being done here is extremely interesting. Additionally: good work-life balance, flexible schedule, parking, and a terrific retirement plan. Very generous with funding for education. A significant amount of interaction with top executives.
Cons
Now I know what it felt like to live in the Soviet Union in the 1970's. Job security, medical benefits, time off...and absolutely no chance of advancement ever. No matter how good or bad you do, the only thing that matters in terms of promotions are years a Draper (many people have 25-50). Most of the people at the top have worked here for most or all of their careers, which really limits the influx of new business practices and ideas.